Not applicable.
1. Field of the Invention
The present invention relates generally to target tracking systems and methods, and more particularly to a method and system that predicts and detects the crossing of two target tracks observed in a bearing versus time coordinate frame.
2. Description of the Prior Art
State-of-the-art sonar systems utilize automated tracking algorithms to track multiple contacts simultaneously. The tracks are typically displayed in a bearing versus time coordinate frame. The sonar operator studies this display and provides critical analysis that will be utilized by other functions such as navigation. Unfortunately, when two tracks (i.e., contacts) have crossed in bearing, many tracking algorithms give inaccurate bearing measurements or completely lose a track. Such misinformation or loss of information severely impairs the sonar operator""s ability to correctly analyze sonar tracking output.
Accordingly, it is an object of the present invention to provide a method and system of predicting and detecting when two target tracks will cross or have crossed in bearing.
Another object of the present invention is to provide a method and system that can alert one to the possibility of a crossing in bearing or an actual crossing in bearing of two target tracks.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, a method and system are provided for predicting and detecting the crossing of two target tracks in a bearing versus time coordinate frame. The method and system use bearing measurements provided every K seconds for each of the two target tracks. The bearing measurements are typically provided by a tracking system. A bearing rate and a projected intercept with a bearing axis of the bearing versus time coordinate frame are determined using bearing measurements for the two target tracks over a most-recently occurring window of time defined by (Jxc3x97K) seconds where J represents the number of samples in a window and is an integer constant that is greater than two. A projected crossing time tc for the two target tracks is determined using the tracks"" bearing rates and projected intercepts. A prediction that the two target tracks will cross results if a first inequality defined as
(ixc3x97K) less than tcxe2x89xa6K(i+J)
is satisfied. A detection that the two target tracks have crossed results if a second inequality defined as
K(ixe2x88x92J)xe2x89xa6tcxe2x89xa6(ixc3x97K)
is satisfied. In both inequalities, i is a counter that is incremented by one every K seconds.